Non-ablative, phase-changeable, optical data storage systems record information in a phase-changeable material that is switchable between at least two detectable states by the application of energy thereto, for example, the application of projected beam energy such as optical energy, particle beam energy, or the like.
The phase-changeable optical data storage material is present in an optical data storage device having a structure such that the optical data storage material is supported by a substrate and encapsulated in encapsulants. The encapsulants may include anti-ablation materials, thermal insulating materials and layers, anti-reflection layers between the projected beam source and the data storage medium, reflective layers between the optical data storage medium and the substrate, and the like. Various layers may perform more than one of these functions. For example, the anti-reflection layer may also be a thermal insulating layer. The thicknesses of the layers, including the layer of optical data storage material, are optimized to minimize the energy necessary for phase change for a given material while retaining the high contrast ratio, high signal to noise ratio, and high stability of the phase-changeable data storage material.
The phase-changeable material is a material capable of being switched from one detectable state to another detectable state by the application of projected beam energy thereto. The phase-changeable material is such that the detectable states may differ in their morphology, relative degree of order, relative degree of disorder, and be detectable therebetween by the electrical conductivity, electrical resistivity, optical transmissivity, optical absorption, optical reflectivity or any combination thereof.
The optical data storage material is typically deposited as a disordered material, for example, by evaporative deposition, chemical vapor deposition, or plasma deposition. Plasma deposition includes sputtering, glow discharge, and plasma chemical deposition. The optical data storage material is usually a multielement chalcogenide alloy, which in most cases, will undergo a change in local order, e.g., a change in local bonding and/or phase separation, to a certain extent upon cycling between detectable states. This means that the erased state may, at least during initial cycles, exhibit variant properties. The resulting, as deposited, disordered material must be formed. That is, the memory material must be conditioned or otherwise prepared (a) to receive data if the data is going to be recorded in a disordered (binary "1") state, and (b) to be stable with respect to changes in local order, e.g., changes in local bonding and/or phase separation, after numerous, subsequent erase and write cycles. As used herein "forming" means converting all of the individual memory cells from the as deposited, quenched from vapor state to an ordered state corresponding to binary "0", which ordered state is stable against further, undesired changes in local order, such as undesired changes in local bonding and/or phase separation, during numerous subsequent erase and write cycles.
Formation requires the conversion of the data storage material from the as-deposited quenched from the vapor, disordered state corresponding to binary "1", to a more ordered state. Formation may be either (1) directly from the as deposited, quenched from the vapor state to the formed (binary "0") state, or (2) from the as deposited, quenched from the vapor state through intermediately ordered states, with subsequent conversion from the ordered state to subsequent, quenched from the liquid, disordered states, and then to the formed (binary "0") state (3) directly from the as deposited, vapor quenched, as deposited state to the formed, quenched from the liquid state. The quenched from the liquid, disordered state after formation is different from the as-deposited, quenched from the vapor, disordered state.
Formation of the deposited material whether by (a) conversion from the as deposited state directly to the formed (binary "0") state, or (b) conversion from the initial disordered state to a laser vitrified, relatively more ordered, i.e., darkened state, with subsequent conversion to and through further disordered states to the formed state having invariant localized bonding and/or phase separation properties, requires an input of certain specific amounts of energy per unit volume of the optical data storage material. This may be accomplished by a laser beam, e.g., a laser beam switchable between power densitities. The laser beam may be a focused laser beam, e.g., the same focused laser beam used in the optical data storage system for erasing (crystallizing) and writing (melting and vitrifying). The laser beam forms one track at a time by passing over the track many times to convert the material on the track from the as-deposited, disordered, material to the more ordered material. Formation, which may include melting and solidification when an intermediate disordered state is formed, requires the balancing of the laser power density, disk rotation speed, total exposure, and number of revolutions per track. If these variables are not properly balanced, the resulting material may not have the proper morphology to serve as the basis of formation. Improper formationc an result in undesired, variant phase separation, large grain size, and poor contrast characteristics. Formation is not only an energy intensive step in the manufacturing process, requiring precise control, but also because it is done one track at a time, a time consuming, low productivity step in the manufacturing process.